The present invention relates to an apparatus and method for removing an edge portion of a moving web in a web processing machine, and particularly a notch portion in a folded web edge of plastic film web for a draw tape bag.
Various products are formed from a plastic sheet material. In forming of the product, the web may be supplied from a roll of indefinite length in a continuous flow to form a series of like products. A typical example is shown in the co-pending application Ser. No. 158,418 of Robert J. Wech, entitled "Draw Tape Bag Forming Method And Apparatus", which was filed on even date herewith and is assigned to a common assignee herewith. Generally, as disclosed therein a roll of a pliable plastic web is mounted in an unwind stand. The plastic web is withdrawn as a flat continuous web and passed through a series of stations for forming a series of draw tape bags. Generally, the flat web is fed into a hem former which is adapted to fold the edges of the web inwardly to form a hem portion. The folded hem is passed through a cutting unit for removing of a peripheral edge notch defining the tape access openings in the draw tape bag. The edge notched web is fed into a tape inserter for receiving of the draw tape, followed by a heat seal unit to seal and form the hems. The hemmed plastic sheet is folded on itself, and passed through a bag forming machine which transversely bonds and severs the web to form a series of the draw tape bags. The web bags are formed with the web moving in a continuous and uninterrupted manner through the machine. Consequently, the cutting or notching apparatus must operate on the web as it moves through the notching apparatus. Various means have been suggested for removal of the edge portion of a web as it moves through a hemming apparatus. For example, U.S. Pat. No. 4,624,654 which issued Nov. 25, 1986 discloses a draw tape bag formed from a continuously moving web. The patent broadly identifies use of a simple punch unit for engaging and severing of the hem edge to form the notch or opening. The punch is actuated in intermittent time sequence through the horizontally moving web to notch the hem along longitudinally spaced locations corresponding to the central location on the top edge of the draw tape bag. A similar bag forming apparatus is disclosed in U.S. Pat. No. 4,664,649 which issued May 12, 1987 and discloses a rotary cutting device for moving through the hem portion to form the notch. The cutter includes a curved flat blade secured to one end of a rotating arm. The edge of the blade is formed as a cutter edge. A motor is connected through a brake and clutch unit to rotate the arm. The motor runs continuously at full operating speed. The brake holds the rotating arm and cutter in a predetermined spaced relation to the moving hem. Whenever a notch is to be formed, the brake is disengaged and clutch is engaged coupling the head to the full speed operating motor. This provides a sudden load on the motor which then serves to accelerate the drive mechanism including the arm and accelerates the arm to move from the standby position through the cutting position. After forming the notch, the clutch is de-energized and the brake is energized to stop and hold the cutter in standby for the next cycle. The assembly including the clutch and brake mechanism is housed in a protective structure adjustable with respect to the edge location. The assembly is difficult to mount and adjust for optimum cutting. Further, the engaging and disengaging of the cutter mechanism with the motor through the brake and clutch mechanism and particularly with the motor at the full speed creates maximum stress on the various members and mechanisms. Such a system will generally require maximum maintenance and reduce the overall anticipated operating life of the mechanism.
The problem is even more significant in a flat web processing system wherein web hems are separately formed and processed, requiring duplicate notchers in forming of a draw tape bag.
Although there are operative devices for edge notching of a web such as the hem of a draw tape plastic bag, there is a need for a more efficient and effective cutting apparatus for forming notches in a continuously moving web and particularly in an edge folded plastic web such as used in forming of draw tape bags.